RNA interference or “RNAi” is a term initially coined by Fire and co-workers to describe the observation that double-stranded RNA (dsRNA) can block gene expression when it is introduced into worms (Fire et al., Nature 391:806-811, 1998). Short dsRNA directs gene-specific, post-transcriptional silencing in many organisms, including vertebrates, and has provided a new tool for studying gene function. RNAi has been suggested as a method of developing a new class of therapeutic agents. However, to date, these have remained mostly as suggestions with no demonstrate proof that RNAi can be used therapeutically.
Transforming growth factor-beta (TGF-beta) isoforms (−1, −2, & −3) are potent cytokines that act in autocrine and paracrine fashion to effect a broad spectrum of biological processes, including proliferation, differentiation, apoptosis, and extracellular matrix production. TGF-beta exerts its biological effects via binding to TGF-beta receptors (types I, II, & III). The local over-expression of TGF-beta in the kidney, liver, or lung mediates the pathophysiology observed in diabetic nephropathy, chronic liver disease, and pulmonary fibrosis, respectively. TGF-beta1 is up-regulated in patients with diabetic nephropathy (for both type 1 or type 2 diabetes) and in animal models of the disease. Antibodies to TGF-beta have been shown to prevent disease in a mouse genetic model of type 2 diabetes (db/db mouse) and antisense targeting a conserved sequence in TGF-beta RNA has been shown to prevent disease in a streptozotocin-diabetic mouse model.
About 100,000 diabetic patients per year are treated for kidney disease in U.S. with health costs of $5.1 billion per year in the U.S. Diabetic nephropathy is the leading cause of end-stage renal disease in the industrialized world. Almost 40% of all new patients with renal failure admitted to renal replacement programs in the U.S have diabetic kidney disease. Albuminuria, proteinuria, serum creatinine, as well as circulating TGF-beta1 plasma levels, can be used as markers for efficacy determination in therapeutic evaluation.
Liver disease affects all age groups and both genders. The condition can be acute or chronic. The major causes of liver diseases in the United States are viruses (hepatitis A, B, C) and alcohol abuse. However, congenital, autoimmune and drug-induced causes are also significant contributors to the origin of liver diseases. Liver diseases disturb hepatic functions as a result of destruction of functional liver tissue and development of fibrosis (scarring), which blocks blood flow through the liver and causes portal hypertension (pressure in the portal vein). Blood flow then seeks an alternative route, leading to dilated swollen veins (varices) in the esophagus that may hemorrhage. Liver disease and portal hypertension also alter kidney function by causing retention of salt and water (ascites), and can induce renal failure (hepatorenal syndrome) and altered mental state (coma). The primary cytokine involved in tissue scaring in chronic liver disease is TGF-beta1. Recently it has been shown in a rat model of liver fibrosis that blocking TGF-beta1 can lead to improvement in liver histology. Further, in chronic Hepatitis C patients who have responded to interferon alpha, decreased levels of TGF-beta1 are associated with improvements in liver fibrosis.
TGF-beta1 has also been implicated in Idiopathic Pulmonary Fibrosis. Similar to liver disease, the mechanisms of action of TGF-beta1 in pulmonary fibrosis involves both induction and inhibition of the degradation of extracellular matrix proteins, leading to the formation of scar tissue. TGF-beta1 mediated cell signaling, primarily at the local site of connective tissue, is anabolic and leads to pulmonary fibrosis and angiogenesis, strongly indicating that TGF-beta1 may be involved in the repair of tissue injury caused by burns, trauma, or surgery. Pulmonary fibrosis, also called Interstitial Lung Disease (ILD), is a broad category of lung diseases that includes more than 130 disorders which are characterized by scarring of the lungs. ILD accounts for 15% of the cases seen by pulmonologists. Some of the interstitial lung disorders include: Idiopathic pulmonary fibrosis, Hypersensitivity pneumonitis, Sarcoidosis, Eosinophilic granuloma, Wegener's granulomatosis, Idiopathic pulmonary hemosiderosis, and Bronchiolitis obliterans. In ILD, scarring or fibrosis occurs as a result of either an injury or an autoimmune process. Approximately 70% of ILD have no identifiable cause and are therefore termed “idiopathic pulmonary fibrosis.” Some of the known causes include occupational and environmental exposure, dust (silica, hard metal dusts), organic dust (bacteria, animal proteins), gases and fumes, drugs, poisons, chemotherapy medications, radiation therapy, infections, connective tissue disease, systemic lupus erythematosus, and rheumatoid arthritis. In its severest form, ILD can lead to death, which is often caused by respiratory failure due to hypoxemia, right-heart failure, heart attack, stroke, blood clot (embolism) in the lungs, or lung infection brought on by the disease.
The use of small interfering nucleic acid molecules targeting transforming growth factor beta (TGF-beta) genes provides a class of novel therapeutic agents that can be used in the treatment of various diseases and conditions associated with undesired TGF-beta signaling, including diabetic nephropathy, chronic liver disease, pulmonary fibrosis, hematopoietic reconstitution, and any other inflammatory, respiratory, autoimmune, and/or proliferative disease, condition, or trait that responds to the level of TGF-beta in a cell, subject or organism, and particularly idiopathic pulmonary fibrosis.